The exchange of oxygen and carbon dioxide between the inspired air and the blood to be oxygenated is done through the pulmonary alveoli which are grouped in racemes surrounded by a network of capillaries where the blood to be ventilated is circulating.
The exterior faces of such walls are covered with a very thin film, monomolecular, of a viscous tensioactive substance which is synthesized by the type II alveoli, which controls the alveoli expansion, reducing the tendency to collapse (that is to say, the occlusion) of the alveoli during the expiration phase.
On the other hand such a film, due to is tensioactive properties, facilitates the displacement of macrophages (alveolaris) that capture foreign elements trapped in this film (inspired particles, bacteria, viruses), that travel along the alveoli surface and move to the bronchial mucociliar zone.
This substance having tensioactives properties that covers the alveoli surface, named pulmonary surfactant (PS) is of complex composition, not completely elucidated; in addition it varies with age, health and also with the extraction method. In general, the PS extract from healthy persons and other mammals contains 90% lipids, 80% of which are phospholipids and the remainder neutral lipids, mainly cholesterol. Phospholypic fraction in mammals in general.
In addition to the lipid fraction mentioned, the PS have a protein fraction from which was extracted and characterized several proteins that have tensioactive properties and complement the lipid tensioactive properties, and these include PS-A, PS-B, PS-C, PS-D, and the like.
When there are not sufficient physiological quantities of PS and/or when the PS film is altered, it presents respiratory problems that produce clinical charts with severe characteristics such as generically denoted respiratory distress syndrome (RDS) and adult respiratory distress syndrome (ARDS).
The patients that exhibit the above mentioned syndrome are treated by providing exogenous PS, a product that is obtained by washing the pulmonary tract of healthy animals (especially pork and in less abundance cows or sheep) with saline solutions and further fractionation, purification and lyophilization. Given that the exogenous PS is an expensive product, the treatment with natural exogenous PS, in general, is limited to the treatment of premature infants.
The high price of the natural exogenous PS has motivated the search for synthetic exogenous surfactants that are less expensive. There are several products with the tensioactive characteristics of natural PS, such as mixtures of dypalmitoilphodphatidylcoline (DPPC), hexadecanol and phyloxapol (Exosurf), phosphatidylglycocerol (ALEC), etc.
Exogenous PS is a product that results from the extraction, by aqueous saline solution from a pig's respiratory system or from a cow or sheep. Also from lung divided in sheets with later fractionation and purification, and in accordance with a sequence of operations of filtration, dialysis, ion exchange chromatography and exclusion chromatography in order to arrive at a lyophilized product or product in dilute solutions with a cost in the order of 4,000 to 5,000 dollars per gram.